Signal outputs for program changes, volume adjustments, end of battery life etc. are customary in present-day hearing systems or, as the case may be, hearing aids according to the publication EP 0 557 847 A1. The signal that is fed out is what is termed a device signal, which is to say a signal generated by the hearing aid itself. A device signal is typically generated in the form of a whistling tone. It is generally possible to set at least the frequency and level of said device signal.